Angle of attack sensor with integral bearing support cage

ABSTRACT

An angle of attack sensor includes a housing having an open end and a closed end. A faceplate is positioned on the open end of the housing. The faceplate comprises an integral bearing support cage that extends into the housing and is configured to accept a first bearing and a second bearing, a periphery at an outer edge of the faceplate, a central opening, and an exterior surface extending from the periphery to the central opening. A vane assembly extends through the central opening of the faceplate. A vane shaft extends into the housing and is connected to the vane assembly, and a rotational position sensor is connected to the vane shaft.

BACKGROUND

The present disclosure relates generally to angle of attack sensors, andmore particularly to angle of attack sensors that utilize a rotatablevane.

Modern aircraft often incorporate air data systems that calculate airdata outputs based on measured parameters collected from various sensorspositioned about the aircraft. For instance, many modern aircraftutilize angle of attack sensors having a rotatable vane that is used todetermine the aircraft angle of attack (i.e., an angle between oncomingairflow or relative wind and a reference line of the aircraft, such as achord of a wing of the aircraft). The angle of attack sensor is mountedto the aircraft such that the rotatable vane is exposed to oncomingairflow about the aircraft exterior. Aerodynamic forces acting on therotatable vane cause the vane to align with the direction of theoncoming airflow (i.e., along a chord extending from a leading edge to atrailing edge of the vane). Rotational position of the vane is sensedand utilized to determine the aircraft angle of attack.

Hindrance of the free rotation of the angle of attack vane orinterference with aerodynamic characteristics of the vane due to icingconditions can degrade the accuracy of angle of attack determinationsderived from the rotational position of the vane. Accordingly, angle ofattack sensors utilizing rotatable vanes typically include heatingelements to prevent accretion of ice on the vane and faceplate. Suchheating elements, however, may utilize a significant portion of anamount of electrical power allotted to the angle of attack sensor duringoperation of the aircraft (i.e., an electrical power budget of the angleof attack sensor). Accordingly, the amount of electrical power utilizedby the heating elements during anti-icing and/or deicing operations isan important consideration in the design of such angle of attacksensors.

SUMMARY

An angle of attack sensor includes a housing having an open end and aclosed end. A faceplate is positioned on the open end of the housing.The faceplate comprises an integral bearing support cage that extendsinto the housing and is configured to accept a first bearing and asecond bearing, a periphery at an outer edge of the faceplate, a centralopening, and an exterior surface extending from the periphery to thecentral opening. A vane assembly extends through the central opening ofthe faceplate. A vane shaft extends into the housing and is connected tothe vane assembly, and a rotational position sensor is connected to thevane shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial side view of an angle of attack sensor with afrustoconical faceplate.

FIG. 1B is a front view of the angle of attack sensor.

FIG. 1C is an isometric view of the angle of attack sensor.

FIG. 2A is a sectional view of the faceplate of the angle of attacksensor.

FIG. 2B is a sectional view of the angle of attack sensor showing thefaceplate having a faceplate heater and showing the bearing supportcage.

FIG. 2C is an isometric bottom view of the faceplate.

FIG. 3A is a top view of the angle of attack sensor showing a collectionefficiency pattern of the faceplate.

FIG. 3B is a top view of the angle of attack sensor showing thetemperature profile of the faceplate heater.

FIG. 4A is a photograph showing the temperature profile of the faceplateheater three seconds after start-up.

FIG. 4B is a photograph showing the temperature profile of the faceplateheater four seconds after start-up.

FIG. 4C is a photograph showing the temperature profile of the faceplateheater five seconds after start-up.

FIG. 4D is a photograph showing the temperature profile of the faceplateheater twenty seconds after start-up.

FIG. 4E is a photograph showing the temperature profile of the faceplateheater twenty-five seconds after start-up.

FIG. 5A is a partial side view of the angle of attack sensor showing thevane having vane heating elements.

FIG. 5B is a sectional view of the vane showing a profile of the vane.

FIG. 6 is a side view of the angle of attack sensor showing arelationship of faceplate slope angle, vane sweep angle, and vaneheight.

DETAILED DESCRIPTION Angle of Attack Sensor Faceplate Geometry (FIGS.1A-1C)

FIG. 1A is a partial side view of angle of attack sensor 10 withfrustoconical faceplate 12. FIG. 1B is a front view of angle of attacksensor 10. FIG. 1C is an isometric view of angle of attack sensor 10.FIGS. 1A, 1B, and 1C will be discussed together. Angle of attack sensor10 includes faceplate 12, housing 14 (having first end 14A and secondend 14B), vane assembly 16, which includes vane hub 18 and vane 20(including root 22 and tip 24), vane shaft connectors 26, andelectronics interface connector 28. Faceplate 12 includes interiorsurface 30, exterior surface 32, opening 34, periphery 36, mountingbores 38, leading edge 40, trailing edge 42, upstream portion 44, anddownstream portion 46. Single-piece faceplate 12 of angle of attacksensor 10 is a heated faceplate. A heater provides heat to faceplate 12,which is made of thermally conductive material. In this embodiment,faceplate 12 is metal, such as aluminum. In alternate embodiments,faceplate 12 may be any suitable thermally conductive material. Housing14 is cylindrical with an annular sidewall between open first end 14Aand closed second end 14B. Faceplate 12 is positioned on open first end14A of housing 14. Vane assembly 16 is adjacent faceplate 12. Vaneassembly 16 rotates about axis A. Vane assembly 16, which includes vanehub 18 and vane 20, has a portion that is positioned within faceplate 12and extends through faceplate 12. More specifically, vane hub 18 ispositioned in faceplate 12. Vane 20 has root 22 at a first end and tip24 at a second end such that vane 20 extends from root 22 to tip 24. Tip24 is opposite root 22. Root 22 of vane 20 is connected to vane hub 18.Root 22 can be integrally formed with vane hub 18, such that vane 20 isintegral to vane hub 18 or otherwise attached to vane hub 18 (e.g., viawelding, brazing, or other connection). Vane hub 18 receives vane shaftconnectors 26. Vane shaft connectors 26 extend through vane hub 18. Afirst end of a rotatable vane shaft is connected to vane hub 18 via vaneshaft connectors 26.

Electronics interface connector 28 extends from housing 14 into aninterior of the aircraft. Electronics interface connector 28 can beconfigured to connect with an aircraft communications data bus, such asa data bus configured to communicate via the Aeronautical Radio,Incorporated (ARINC) 429 communications protocol or other communicationsprotocols. In other examples, electronics interface connector 28 carrieselectrical signals (e.g., analog alternating current voltages) from arotational position sensor positioned within housing 14 and configuredto sense rotation of a shaft connected to vane assembly 16, as isfurther described below. In some examples, electronics interfaceconnector 28 carries electrical power to angle of attack sensor 10 foruse by heating elements included within vane 20 and/or faceplate 12and/or electrical components included within housing 14. In otherexamples, angle of attack sensor 10 includes additional connectors(i.e., separate from electronics interface connector 28) configured tocarry electrical power and/or additional electrical and/or communicativesignals, though additional connectors need not be present in allexamples.

Faceplate 12 has interior surface 30 facing toward housing 14, or towardan interior of angle of attack sensor 10. Exterior surface 32 offaceplate 12 is the surface opposite interior surface 30, or the surfaceof faceplate 12 that faces external airflow. At its center, faceplate 12has circular opening 34, which extends from interior surface 30 toexterior surface 32. Vane assembly 16 extends through opening 34 offaceplate 12, or protrudes from faceplate 12 at opening 34. Morespecifically, vane hub 18 is positioned in opening 34. Opening 34 isconcentric with periphery 36. In alternate embodiments, opening 34 maybe non-concentric with periphery 36. Periphery 36 of faceplate 12 is theoutermost part of faceplate 12. As such, periphery is the circular outeredge, or circumference, of faceplate 12. Faceplate 12 meets the aircraftskin at periphery 36. Exterior surface 32 of faceplate 12 extends fromperiphery 36 to central opening 32. Mounting bores 38 are located aroundperiphery 36 of faceplate 12. Mounting bores 38 extend through faceplate12 from interior surface 30 to exterior surface 32. In this embodiment,faceplate 12 has eight mounting bores 38. In alternate embodiments,faceplate may have any number of mounting bores 38. Leading edge 40 is afore portion of periphery 36 of faceplate 12, and trailing edge 42 is anaft portion of periphery 36 of faceplate 12. Upstream portion 44 is aportion of faceplate 12 that is upstream with respect to oncomingairflow when angle of attack sensor 10 is installed on an aircraft.Upstream portion 44 is upstream of vane assembly 16. Downstream portion46 is a portion of faceplate 12 that is downstream from upstream portion44 (and downstream with respect to oncoming airflow) when angle ofattack sensor 10 is installed on an aircraft. Downstream portion 46 isadjacent upstream portion 44. Downstream portion 46 is downstream ofvane assembly 16.

Exterior surface 32 of faceplate 12 continuously inclines, or has asloped profile, from periphery 36 to opening 34 such that a height offaceplate 12 at opening 34 is greater than the height of faceplate 12 atperiphery 36. Faceplate 12 progressively increases in height fromperiphery 36 to opening 34. As such, faceplate 12 surrounds vane hub 18and exterior surface 32 of faceplate 12 slopes downward and outward fromopening 34 to periphery 36. Thus, an exterior surface of vane hub 18 androot 22 of vane 20 are above the skin of the aircraft. In thisembodiment, the sloped profile, or continuous incline, of faceplate 12is axisymmetric and has the same axis A as vane assembly 16. Inalternate embodiments, the sloped profile, or continuous incline, offaceplate 12 may be non-axisymmetric and/or have a different axis thanaxis A of vane assembly 16. In this embodiment, faceplate 12 has afrustoconical exterior surface 32. In alternate embodiments, faceplate12 may have an exterior surface 32 that is ellipsoidal, hemispherical,trapezoidal, another convex shape, or any other suitable shape. Infurther alternate embodiments, exterior surface 32 of faceplate 12 mayhave exterior surface 32 with a continuous incline, or a sloped profile,only at upstream portion 44 such that faceplate 12 has sloped upstreamportion 44 and flat downstream portion 46.

Angle of attack sensors 10 are installed on the exterior of an aircraftand mounted to the aircraft via fasteners, such as screws or bolts,which interface with mounting bores 38 on faceplate 12. As a result,periphery 36 of faceplate 12 is about flush with the skin of theaircraft, and housing 14 extends within an interior of the aircraft.Vane 20 extends outside an exterior of the aircraft and is exposed tooncoming airflow, causing vane 20 and vane hub 18 of vane assembly 16 torotate with respect to faceplate 12 via a series of bearings withinangle of attack sensor 10. Vane assembly 16 rotates based on the anglethe aircraft is flying at relative to the oncoming airflow. Morespecifically, vane 20 rotates to be parallel with, or align with,oncoming airflow. Vane 20 causes vane hub 18 to rotate. Rotation of vanehub 18 causes rotation of a vane shaft, which is within housing 14 andcoupled to a rotational sensor that measures the local angle of attackor angle of the airflow relative to the fixed aircraft structure. Theangle of attack measurement is communicated to an aircraft flightcomputer via electronics interface connector 28.

When the aircraft is in flight, faceplate 12 is exposed to externalairflow, which is cold and often contains water droplets or iceparticles. Periphery 36 of faceplate 12 is also adjacent the aircraftskin, which is below freezing. Heated faceplate 12 conducts heat to therotating components of angle of attack sensor 10, such as vane assembly16. Ice particles from oncoming airflow directly impinge on heatedexterior surface 32 of faceplate 12 and melt or bounce off faceplate 12.Faceplate 12 eliminates icing that can result from both directimpingement and runback of the melted ice particles or liquid water.

A first failure mode avoided by angle of attack sensor 10 is runbackicing, where liquid water or ice that has melted on a heated faceplateruns back to a colder surface of the faceplate, refreezes, and growsinto a large ice horn that impacts angle of attack measurement. A secondfailure mode avoided by angle of attack sensor 10 is step icing, or icegrowth at the interface between the faceplate and the aircraft skin.

The continuous incline of exterior surface 32 of faceplate 12 allows iceand water to shed from faceplate 12, redirecting the melted iceparticles or liquid water to eliminate runback.

The frustoconical shape of faceplate 12 also causes a static pressurebulge, or an increase in static pressure on leading edge 40 of faceplate12. As a result, incoming water droplets are diverted to the sides offaceplate 12 and vane 20, creating a shadowing effect aft of vane 20 attrailing edge 42 of faceplate 12 where periphery 36 meets the aircraftskin. Ice is prevented from accumulating aft of vane 20 where any step,or height difference, between faceplate 12 and the aircraft skin wouldotherwise result in ice growth.

Additionally, the frustoconical shape of faceplate 12 causes flowseparation at downstream portion 46 of faceplate 12, or a trailing eddy.As such, any water droplets from downstream portion 46 are wicked away,preventing water droplets from freezing and accumulating into icegrowths.

Further, the slope of exterior surface 32 of faceplate 12 causesfaceplate 12 to project into the airstream, which shields downstreamportion 46 of faceplate 12 from being directly hit by water droplets.Because an exterior surface of vane hub 18 is not flush with an entiretyof exterior surface 32 of faceplate 12 and is above the skin of theaircraft, incoming water droplets are more likely to continue downstreamthan accrete on vane hub 18, which is farther off the boundary layer,diminishing the impact of any ice build-up.

On heated faceplates having a flat outer surface, impinging waterrunback can refreeze and form ice growths on the colder downstreamportion of the faceplate. The ice accumulation forms a shape behind thevane that becomes large enough to disrupt airflow and cause errors inmeasurements of the angle of attack sensor. Additionally, impingingwater runback can freeze and accumulate at the interface between thefaceplate and the aircraft skin, which is not heated. Such step icingaffects the accuracy of the angle of attack sensor measurements.Faceplate 12 mitigates both (1) ice accumulation on downstream portion46 of faceplate 12 aft of vane 20 and (2) ice accumulation at theinterface of faceplate 12 and the aircraft skin.

Angle of Attack Sensor Bearing Cage (FIGS. 2A-2C)

FIG. 2A is a sectional view of faceplate 12 of angle of attack sensor10. FIG. 2B is a sectional view of angle of attack sensor 10 showingfaceplate 12 having faceplate heater 58 and showing bearing support cage60. FIG. 2C is an isometric bottom view of faceplate 12. FIGS. 2A, 2B,and 2C will be discussed together. Angle of attack sensor 10 includesfaceplate 12, vane assembly 16 (shown in FIG. 2A), which includes vanehub 18 and vane 20, vane shaft 48 (shown in FIG. 2A), rotating interfacecavity 50, rotational position sensor 52 (shown in FIG. 2B), outerbearing 54 (shown in FIG. 2A), inner bearing 56 (shown in FIG. 2A), andfaceplate heater 58 (shown in FIG. 2B). Faceplate 12 includes interiorsurface 30, exterior surface 32, opening 34, and bearing support cage60, which includes outer support 62, inner support 64, supporting leg66, supporting leg 68, support cavity 70, outer bearing bore 72, andinner bearing bore 74.

Angle of attack sensor 10 has the same structure and function asdescribed with respect to FIGS. 1A, 1B, and 1C. A first end of rotatablevane shaft 48 is connected to vane hub 18 via vane shaft connectors 26(shown in FIG. 1C). More specifically, vane shaft connectors 26 extendthrough vane hub 18 to connect vane hub 18 to vane shaft 48. Vane shaft48 is rotatable about axis A (shown in FIG. 2A). Vane 20, vane hub 18,and vane shaft 48 are configured to rotate together. Vane hub 18 ispositioned in rotating interface cavity 50, which is a space withinopening 34 of faceplate 12. Rotating interface cavity 50 extends fromexterior surface 32 of faceplate 12. A first end of vane shaft 48extends through rotating interface cavity 50. A second end of vane shaft48 extends into housing 14 (shown in FIGS. 1A-1C). Rotational positionsensor 52 is connected to the second end of vane shaft 48 via a resolvershaft. In one embodiment, rotational position sensor 52 is a resolverthat senses rotational position of vane shaft 48. Rotational positionsensor 52 is positioned within housing 14. In alternate embodiments,rotational position sensor 52 may be an encoder, synchro, lineartransformer, rotary variable differential transformer (RVDT),potentiometer, or any other suitable sensor that can sense relative(i.e., incremental) and/or absolute angular position of vane shaft 48.Vane shaft 48 extends through outer bearing 54 and into inner bearing56. Outer bearing 54 is adjacent rotating interface cavity 50. Thesecond end of vane shaft 48 is within inner bearing 56. Faceplate heater58 is positioned on an inner surface of, or embedded in, faceplate 12.Faceplate heater 58 may comprise a plurality of heater chips, heaterrings, or any other suitable heating elements. Faceplate heater 58extends around vane assembly 16. Faceplate heater 58 is aself-regulating heater.

Bearing support cage 60 is an integral part of faceplate 12. Bearingsupport cage 60 is an inner central portion of faceplate 12 that extendsinto housing 14. Bearing support cage 60 has outer support 62 adjacentopening 34 and rotating interface cavity 50 and inner support 64adjacent rotational position sensor 52. Supporting leg 66 extends fromouter support 62 to inner support 64. Supporting leg 68 extends fromouter support 62 to inner support 64 opposite supporting leg 66. Supportcavity 70 is a space between outer support 62 and inner support 64 andbetween supporting leg 66 and supporting leg 68. Outer bearing bore 72is an opening that extends through outer support 62 and is configured toaccept outer bearing 54. Inner bearing bore 74 is an opening thatextends through inner support 64 and is configured to accept innerbearing 56. Outer bearing bore 72 and inner bearing bore 74 are axiallyaligned. Outer bearing bore 72 and inner bearing bore 74 are machinedfrom the same axis on the same machine without moving faceplate 12 sothat misalignment of outer bearing bore 72 and inner bearing bore 74 isavoided. Outer bearing bore 72 and inner bearing bore 74 are cut in thesame orientation from a single piece of metal, such as aluminum, via aCNC machining process. Rotating interface cavity 50 is also machined atthe same time and along the same axis as outer bearing bore 72 and innerbearing bore 74. A complex undercut geometry forms support cavity 70.

Rotational position sensor 52 is connected to vane shaft 48 and measuresangular rotation of vane shaft 48 and vane assembly 16 to determine thelocal angle of attack. Faceplate heater 58 provides heat to faceplate 12near rotating vane assembly 16 and vane shaft 48. Outer support 62supports, or holds, outer bearing 54, and inner support 64 supports, orholds, inner bearing 56. Vane shaft 48 extends from rotating interfacecavity 50, through outer bearing bore 72, through support cavity 70, andinto inner bearing bore 74. Support cavity 70 provides space for acounterweight (not shown) connected to vane shaft 48 and heater wires(not shown) to freely rotate unobstructed between outer support 62 andinner support 64.

Bearing support cage 60 has outer bearing bore 72 and inner bearing bore74 that are machined from a single piece of metal, such as aluminum, onthe same machine without repositioning faceplate 12 so that both boringprocedures are performed on the same axis. As a result, precisealignment between outer bearing 54 and inner bearing 56 on single-piecemonolithic faceplate 12 is achieved. As such, bearing support cage 60ensures bearing alignment, which is critical because of the short lengthof vane shaft 48 and thus short distance between outer bearing 54 andinner bearing 56.

Further, bearing support cage 60 provides a direct thermal conductionpath from faceplate heater 58 to rotational position sensor 52. Heat isrouted from faceplate heater 58 to rotational position sensor 52 viadirect conduction through bearing support cage 60, with no other thermalinterfaces. Heat conduction is tailored such that only the necessaryamount of heat is bled from the faceplate heater 58 through bearingsupport cage 60 to rotational position sensor 52, minimizing the amountof power used by faceplate heater 58. Tailoring heat conduction resultsin less heat being lost to the cold oncoming airflow.

Traditionally, a series of parts stack up to create the structure tohold the outer bearing and the inner bearing. As angle of attack sensorsare mounted in locations where aircraft interior compartments arerelatively small, the overall length of the angle of attack sensor fromthe interior surface of the faceplate to the electrical interfaceconnector must be kept to a minimum. Therefore, the vane shaft of theangle of attack sensor is short in length, requiring a stack up ofmultiple parts over a short distance. This stack up creates a series oftolerances that may compound to result in misalignment between the outerbearing and the inner bearing. Bearing misalignment can cause higherfriction and spring-back that result in reduced overall performance(sensitivity and accuracy) of the angle of attack sensor. Misalignmentis very difficult to correct and in some instances parts or completeassemblies are scrapped due to the inability to achieve statedperformance.

Near perfect alignment (less than 0.001 inch, or 0.0254 millimeters,center to center relative tolerance) between outer bearing 54 and innerbearing 56 is achieved via bearing support cage 60, eliminating any riskof shaft bending due to misalignment and keeping friction to a minimum,which results in improved unit accuracy and sensitivity.

Further, traditional angle of attack sensors sometimes include specificheaters for heating the rotational position sensor. However, with modernicing requirements, the heaters have been redeployed as faceplateheaters, leaving the rotational position sensors less temperaturecontrolled than in the past. Due to the complexity of heaterarchitectures and the need to identify heater malfunction, simply addinganother heater is less desirable. Additionally, angle of attack sensor10 is cold prior to flight and must be fully operational typicallywithin a short amount of time after power-on, resulting in a short warmup time for rotational position sensor 52.

A direct conduction path from faceplate heater 58 to rotational positionsensor 52 allows heating of rotational position sensor 52 within therequired warm up time without requiring a tertiary heater, or anadditional heater specifically for heating rotational position sensor52, which requires additional power, reduces overall reliability, and isless cost-effective. The single-piece design of faceplate 12 alsoreduces parasitic losses. As a result, more power from the limitedoverall power budget of angle of attack sensor 10 can be used to reduceicing and ensure performance of angle of attack sensor 10 in icingconditions.

As mechanical devices with varying coefficients of thermal expansionamong components, angle of attack sensors are susceptible to operationaltemperature differences. As a result, it is difficult to achieve acommon stated accuracy over the total temperature range of operation.Providing a direct thermal conduction path from faceplate heater 58 torotational position sensor 52 allows angle of attack sensor 10 toutilize faceplate heater 58 positioned for anti-icing to reduce theoperational temperature variation range of rotational position sensor 52(for example, increasing the lower bound from −55 degrees Celsius to 0degrees Celsius), allowing rotational position sensor 52 to achieve atighter accuracy over the entire operational environmental envelope. Byutilizing self-regulating heaters instead of fixed resistance heaters,there is no increase to the upper temperature limit.

Angle of Attack Sensor Faceplate Heating Pattern (FIGS. 3A-4E)

FIG. 3A is a top view of angle of attack sensor 10 showing collectionefficiency pattern C of faceplate 12. FIG. 3B is a top view of angle ofattack sensor 10 showing temperature profile T of faceplate heater 58.FIGS. 3A and 3B will be discussed together. Angle of attack sensor 10includes faceplate 12, vane assembly 16, which includes vane hub 18 andvane 20 (including root 22 and tip 24). Faceplate 12 includes exteriorsurface 32, opening 34, periphery 36, leading edge 40, trailing edge 42,upstream portion 44, and downstream portion 46. Collection efficiencypattern C includes first zone 76, second zone 78, third zone 80, fourthzone 82, fifth zone 84, sixth zone 86, and seventh zone 88. Temperatureprofile T includes first temperature zone 90, second temperature zone92, third temperature zone 94, fourth temperature zone 96, fifthtemperature zone 98, sixth temperature zone 100, and seventh temperaturezone 102.

Angle of attack sensor 10 has the same structure and function asdescribed with respect to FIGS. 1A-2C. As shown in FIG. 4A,frustoconical faceplate 12 has collection efficiency pattern C, whichillustrates different zones that represent different areas of faceplate12 with different collection efficiencies. A collection efficiencyindicates the risk of ice growth on exterior surface 32 of faceplate 12from ice crystals, water molecules, or other particles in the airflowtraveling over faceplate 12. The shape, or sloped profile, of faceplate12 determines collection efficiency pattern C of faceplate 12.

In this embodiment, collection efficiency pattern C of faceplate 12 hasfirst zone 76, second zone 78, third zone 80, fourth zone 82, fifth zone84, sixth zone 86, and seventh zone 88 that form a whale tail, ortrapezoidal, shape on exterior surface 32 of faceplate 12. First zone 76is at upstream portion 44 of faceplate 12 near leading edge 40. Secondzone 78 surrounds first zone 76. Third zone 80 is adjacent second zone78, having a strip on either side of second zone 78 that extends andexpands from opening 34 to periphery 36. As such, third zone 80 divergestoward leading edge 40 of faceplate 12. Fourth zone 82 has two strips,each strip adjacent a strip of third zone 80 and extending and expandingfrom opening 34 to periphery 36. As such, fourth zone 82 diverges towardleading edge 40 of faceplate 12. Fifth zone 84 has two strips, eachstrip adjacent a strip of fourth zone 82 and extending and expandingfrom opening 34 to periphery 36. As such, fifth zone 84 diverges towardleading edge 40 of faceplate 12. Sixth zone 86 has two strips, eachstrip adjacent a strip of fifth zone 84 and extending and expanding fromopening 34 to periphery 36. As such, sixth zone 86 diverges towardleading edge 40 of faceplate 12. First zone 76, second zone 78, thirdzone 80, fourth zone 82, fifth zone 84, and sixth zone 86 are alllocated at upstream portion 44 of faceplate 12, upstream of vane 20.Seventh zone 88 is adjacent both strips of sixth zone 86 and is locatedat downstream portion 46 of faceplate 12, including near trailing edge42. First zone 76 is most likely to accumulate ice. Seventh zone 88 hasthe lowest propensity for ice growth. The likelihood of ice accumulationon faceplate 12 decreases from first zone 76 to seventh zone 88. Inalternate embodiments, faceplate 12 may have a different shape, asindicated above with respect to FIGS. 1A-1C, and thus may have adifferent collection efficiency pattern C with different zones.

As shown in FIG. 3B, Temperature profile T illustrates the heatingpattern generated by heating elements of faceplate heater 58 (shown inFIG. 2B) on an interior surface of, or embedded within, faceplate 12,which is derived from collection efficiency pattern C of faceplate 12.Temperature profile T of FIG. 3B illustrates the temperature profile offaceplate 12 within a few seconds of faceplate heater 58 being poweredon. Faceplate heater 58 is comprised of multiple heating elementsmounted on faceplate 12 and distributed asymmetrically around vaneassembly 16 to address icing concerns. Faceplate heater 58 has heatingelements arranged around vane hub 18 of vane assembly 16. Additionalheating elements of faceplate heater 58 are also positioned upstream ofvane assembly 16, toward upstream portion 44 and leading edge 40 offaceplate 12. Heating elements of faceplate heater 58 are placed aroundvane assembly 16 to achieve the heat distribution of temperature profileT on faceplate 12.

Temperature profile T has first temperature zone 90, second temperaturezone 92, third temperature zone 94, fourth temperature zone 96, fifthtemperature zone 98, sixth temperature zone 100, and seventh temperaturezone 102 along exterior surface 32. First temperature zone 90 is atupstream portion 44 of faceplate 12 near a leading edge of vane hub 18.Second temperature zone 92 surrounds first temperature zone 90 atupstream portion 44. Third temperature zone 94 is adjacent secondtemperature zone 92 and surrounds vane hub 18. Fourth temperature zone96 is adjacent and surrounds third temperature zone 94. Fifthtemperature zone 98 is adjacent and surrounds fourth temperature zone96. Sixth temperature zone 100 is adjacent and surrounds fifthtemperature zone 98. Seventh temperature zone 102 is adjacent andsurrounds sixth temperature zone 100. Seventh temperature zone 102extends from sixth temperature zone 100 to periphery 36 of faceplate 12.As such, third temperature zone 94, fourth temperature zone 96, fifthtemperature zone 98, sixth temperature zone 100, and seventh temperaturezone 102 all surround vane hub 18.

First temperature zone 90 has the highest temperature among the zones.Temperature decreases from first temperature zone 90 to seventhtemperature zone 102 or from opening 34 to periphery 36. Some heatconduction still occurs within seventh temperature zone 102.Temperatures within each of first temperature zone 90, secondtemperature zone 92, third temperature zone 94, fourth temperature zone96, fifth temperature zone 98, sixth temperature zone 100, and seventhtemperature zone 102 have some variation, with the amount of variationdecreasing from first temperature zone 90 to seventh temperature zone102.

As seen in FIG. 3A, faceplate 12 has a higher collection efficiency atupstream portion 44 near leading edge 40 of faceplate 12, indicatingthat ice or water particles are more likely to adhere to and form icegrowths on leading edge 40 of conical exterior surface 32 of faceplate12 than trailing edge 42 of faceplate 12. Temperature profile T isdesigned to address the icing concerns associated with collectionefficiency pattern C. Because downstream portion 46 of faceplate 12,located in seventh zone 88, has a very low collection efficiency, lessheat is needed at downstream portion 46 of faceplate 12, which islocated in seventh temperature zone 102. As such, more power for heat isfocused on upstream portion 44 of faceplate 12 than downstream portion46 of faceplate 12, particularly near the leading edge of vane hub 18.Variation in collection efficiencies throughout collection efficiencypattern C on faceplate 12 results in an asymmetric layout of heatingelements of faceplate heater 58 to direct heat only where needed andthus use power efficiently. As seen in FIG. 3B, faceplate heater 58maintains heat around an entire circumference of rotating vane assembly16, preventing water and ice particles from traveling beneath vane hub18, freezing, and locking vane assembly 16. Faceplate heater 58 also hasheating elements arranged to provide a higher concentration of heat tofaceplate 12 upstream of vane assembly 16.

Faceplate heater 58 creates temperature profile T of frustoconicalfaceplate 12 based on collection efficiency pattern C of faceplate 12 toprovide efficient heating of faceplate 12, and thus enable efficient useof power.

FIGS. 4A-4E are photographs showing the progression of temperatureprofiles illustrating the heating pattern generated by heating elementsof faceplate heater 58 on faceplate 12 over time. FIGS. 4A-4E are aseries of photographs taken from three seconds to twenty-five secondsafter start-up showing the change in the heating pattern similar to thatshown in FIG. 3B. FIG. 4A shows the temperature profile three secondsafter start-up. FIG. 4B shows the temperature profile four seconds afterstart-up. FIG. 4C shows the temperature profile five seconds afterstart-up. FIG. 4D is shows the temperature profile twenty seconds afterstart-up. FIG. 4E shows the temperature profile twenty-five secondsafter start-up. In FIGS. 4A-4E, the lighter the color, the higher thetemperature. As illustrated in the photos of FIGS. 4A-4E, the heatingpattern is growing and intensifying over a short amount of time afterstart-up, when power to the heating elements of faceplate heater 58 isturned on.

Angle of Attack Sensor Vane Profile (FIGS. 5A-5B)

FIG. 5A is a partial side view of angle of attack sensor 10 showing vane20 having vane heating elements 114A-114I. FIG. 5B is a sectional viewof vane 20 showing a profile of vane 20. FIGS. 5A and 5B will bediscussed together. Angle of attack sensor 10 includes faceplate 12,vane assembly 16, which includes vane hub 18 and vane 20 (including root22, tip 24, leading edge 104, trailing edge 106, first lateral face 108,second lateral face 110, and chord 112), and vane heating elements114A-114I (shown in FIG. 4A). Faceplate 12 includes opening 34.

Angle of attack sensor 10 has the same structure and function asdescribed with respect to FIGS. 1A-3B. Vane 20 has leading edge 104extending from root 22 to tip 24 at an upstream portion of vane 20 andtrailing edge 106 extending from root 22 to tip 24 at a downstreamportion of vane 20, opposite leading edge 104. First lateral face 108and second lateral face 110 of vane 20 each extend from leading edge 104to trailing edge 106, second lateral face 110 being opposite firstlateral face 108. First lateral face 108 and second lateral face 110 aresymmetric about chord 112 that defines a symmetrical center betweenfirst lateral face 108 and second lateral face 110. Chord 112 of vane 20extends in a direction from leading edge 104 to trailing edge 106 andbisects first lateral face 108 and second lateral face 110.

The outer surface profile of each of first lateral face 108 and secondlateral face 110 is both nonlinear and geometrically convex from leadingedge 104 to transition point T. As such, vane 20 has a symmetric NACA(National Advisory Committee for Aeronautics) profile from leading edge104 to transition point T. Transition point T is at the tangent to thewidest point of the symmetric geometrically convex outer surfaceprofile, or NACA profile, of first lateral face 108 and second lateralface 110. Each of first lateral face 108 and second lateral face 110extends or flares out from transition point T to trailing edge 106 sothat vane has a diverging wedge shape from transition point T totrailing edge 106. The diverging wedge shape has an angle of up to 45degrees, and preferably up to 25 degrees. As such, vane 20 has a wedgeprofile extending from the NACA profile. Thus, first lateral face 108and second lateral face 110 each have a forward section with an outersurface profile that is nonlinear and geometrically convex from leadingedge 104 to an intermediate chord location (transition point T) and anaft section with an outer surface profile that extends out to form adiverging wedge shape that extends from the intermediate chord location(transition point T) to trailing edge 106. First lateral face 108 andsecond lateral face 110 form a truncated symmetrical NACA profile andwedge-like profile. First lateral face 108 and second lateral face 110of the wedge-like profile form an angle equal to or between 0 degrees(such that the wedge-like profile is parallel to the direction ofairflow) and 45 degrees, and preferably between 0 degrees and 25degrees. As shown in FIG. 5A, vane heating elements 114A-114I aredisposed within vane 20 between first lateral face 108 and secondlateral face 110 proximate leading edge 104 to provide heat to vane 20for anti-icing and/or deicing operations. Vane heating elements114A-114G each have a forward end disposed at a distance from leadingedge 104 of vane 20 that is less than ten percent of a length of chord112 of vane 20.

In this embodiment, vane 20 has nine separate heating elements (vaneheating elements 114A-114I) extending from a location proximate root 22to a location proximate tip 24. In alternate embodiments, vane 20 mayinclude any number of heating elements. For example, vane 20 may includea single vane heating element disposed within vane 20 from a locationproximate root 22 to a location proximate tip 24 to provide heat to vane20 during anti-icing and/or deicing operations. Vane heating elements114A-114I can be self-regulating heating elements (e.g., self-regulatingchip heaters) or heating elements that are controlled via continuous orpulsed electrical current. In some examples, vane heating elements114A-114I can be thermostatically controlled to achieve and/or maintaina target temperature. Electrical power for vane heating elements114A-114I is provided by a power supply (e.g., received via an externalpower source) and routed through, e.g., vane shaft 48 (shown in FIG. 2A)and between first lateral face 108 and second lateral face 110 to vaneheating elements 114A-114I.

In operation, air flowing over vane 20 in a direction from leading edge104 to trailing edge 106 acts on first lateral face 108 and secondlateral face 110 to cause vane 20 to rotate such that pressuresexperienced by first lateral face 108 and second lateral face 110equalize and chord 112 aligns with a direction of the oncoming airflow.Rotation of vane 20 causes corresponding rotation of vane hub 18 andvane shaft 48. Rotational position sensor 52 measures the rotationalposition (e.g., relative and/or absolute rotational position) of vaneshaft 48 and communicates the measured position signal to an externaldevice, such as an air data computer, stall warning computer, dataconcentrator unit, aircraft display, or other external device via anelectronic communication device within housing 14. Vane heating elements114A-114I provide heat to vane 20 during operation to prevent accretionof ice on vane 20. An outer surface profile of each of first lateralface 108 and second lateral face 110 decreases an amount of heatdissipation from vane 20, thereby decreasing an amount of electricalcurrent required by vane heating elements 114A-114I to providesufficient heat to vane 20 for the anti-icing and/or deicing operations.

Vane 20 has a NACA profile extending downstream from leading edge 104 toa wedge-like profile extending from the NACA profile the trailing edge106, the NACA and wedge profiles meeting at transition point T. Thetransition from the NACA profile to the wedge-like profile occurs at thepoint of maximum thickness of the symmetrical NACA profile of vane 20.Leading edge 104 having a NACA profile allows vane heating elements114A-114I to be closer to the surface of leading edge 104, resulting inice-free performance of vane 20. The wedge-like profile makes vane 20more stable and accurate at high Mach speeds. The overall length of vane20 (from leading edge 104 to trailing edge 106) is kept short, whichresults in less surface area to heat and thus ice-free performance.

Angle of attack sensors generally adopt a wedge profile that tapers to asharper leading edge, which is inherently stable and offers highaccuracy in flight conditions. However, that profile has provendifficult to certify to increasingly stringent icing conditions withoutalso drawing excessive power as it is difficult to heat the leading edgeof a traditional wedge design to keep it ice free across all icingconditions. A NACA vane profile has excellent icing performance, due tothe NACA shape allowing vane heating elements to be installed in closeproximity to the leading edge. However, it was discovered that this NACAprofile can be unstable at High Mach numbers (0.9-1.0).

Vane 20 has a modified NACA profile to avoid flow separation andincrease stability by adding material to form a wedge shape aft of thetransition point T. As a result, vane 20 maintains an almost identicallevel of icing performance (ice-free) and is stable at High Mach numbers(0.9-1.0). Thus, this combination provides both optimal anti-icingperformance and aerodynamic performance.

Angle of Attack Sensor Interchangeability (FIG. 6)

FIG. 6 is a side view of angle of attack sensor 10 showing arelationship of faceplate slope angle A, vane sweep angle S, and vaneheight H. Angle of attack sensor 10 includes faceplate 12, vane assembly16, which includes vane hub 18 and vane 20 (including root 22 and tip24), and leading edge 76. Faceplate 12 includes exterior surface 32,opening 34, periphery 36, leading edge 40, upstream portion 44, anddownstream portion 46.

Angle of attack sensor 10 has the same structure and function asdescribed with respect to FIGS. 1A-5B. Faceplate slope angle A is theslope of exterior surface 32 of faceplate 12 from periphery 36 toopening 34. Faceplate slope angle A is equal to or between 6 degrees and30 degrees, and is preferably equal to or between 6 degrees and 12degrees. Faceplate slope angle A is great enough to have the ability toshed ice particles and/or water droplets and lower the risk of stepicing at trailing edge 42 of faceplate 12 and low enough to not increasewater droplet collection at leading edge 40 of faceplate 12, which wouldrequire additional power to remain ice free. Vane sweep angle S is theangle between leading edge 76 of vane 20 and a line perpendicular tovane hub 18. Vane sweep angle S is greater than zero. Vane 20 extendstoward downstream portion 46 of faceplate 12 as a result of vane sweepangle S. Vane height H is the height of vane 20, or the distance betweenthe horizontal of root 22 and the horizontal of tip 24. The greater thefaceplate slope angle A, the shorter the vane height H. The shorter thevane height H, the greater the vane sweep angle S, in order to generatethe required torque. In an example embodiment, faceplate slope angle Ais 8 degrees, vane height H is 71 mm, and vane sweep angle S is 38degrees. The distance from tip 24 of vane 20 to the skin of the aircraftis between 3.1 and 3.2 inches, and preferably 3.166 inches.

The effects of vane sweep angle S and vane height H, in addition toother aspects of vane shape, can be used to achieve interchangeabilitybetween vanes of different angle of attack sensors having variousconfigurations. To ensure accuracy of angle of attack sensor 10, vaneheight H or the distance from the aircraft is critical. Vane heights Hthat are too long or too short impact the accuracy of angle of attacksensor 10 as a function from the aircraft skin. Each of vane sweep angleS, vane height H, and faceplate slope angle A can be varied to produce avane that is interchangeable with different vanes of various angle ofattack sensors. For example, vane sweep angle S can be modified whilevane height H may remain at a predetermined value in order to achieverequired sensitivity.

As part of normal aircraft certification, the angle of attack vaneoutput is calibrated for local flow effects across the flight envelope.Those calibration tables are typically located within the ADIRUs (AirData Inertial Reference Unit) onboard the aircraft and any change tothose devices is extremely expensive and complicated. Previously,interchangeability design levers were not completely understood. Angleof attack configuration to configuration interchangeable performance isachieved through modifying vane height H and/or vane sweep angle S.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

An angle of attack sensor includes a housing having an open end and aclosed end; a faceplate positioned on the open end of the housing, thefaceplate comprising: an integral bearing support cage that extends intothe housing and is configured to accept a first bearing and a secondbearing; a periphery at an outer edge of the faceplate; a centralopening; and an exterior surface extending from the periphery to thecentral opening; a vane assembly extending through the central openingof the faceplate; a vane shaft that extends into the housing and isconnected to the vane assembly; and a rotational position sensorconnected to the vane shaft.

The angle of attack sensor of the preceding paragraph can optionallyinclude, additionally and/or alternatively, any one or more of thefollowing features, configurations and/or additional components:

The bearing support cage comprises an outer bearing bore configured toaccept the first bearing and an inner bearing bore configured to acceptthe second bearing.

The outer bearing bore and the inner bearing bore are axially aligned.

The outer bearing bore and the inner bearing bore are axially alignedsuch that the tolerance between a center of the outer bearing bore and acenter of the inner bearing bore is less than 0.001 inch (0.0254millimeters).

The outer bearing bore and the inner bearing bore are machined from asingle piece of metal on the same machine without repositioning thefaceplate.

The metal is aluminum.

The bearing support cage further comprises: an outer support adjacentthe central opening, the outer bearing bore extending through the outersupport; and an inner support adjacent the rotational position sensor,the inner bearing bore extending through the inner support.

The bearing support cage further comprises a supporting leg extendingfrom the outer support to the inner support.

The bearing support cage further comprises a support cavity between theouter support and the inner support.

The vane shaft extends through the outer bearing bore, through thesupport cavity, and into the inner bearing bore.

A faceplate heater positioned on an inner surface of the faceplate andextending around the vane assembly.

The bearing support cage provides a direct thermal conduction path fromthe faceplate heater to the rotational position sensor.

The faceplate heater comprises a plurality of heating elements mountedon the faceplate and arranged to provide a higher concentration of heatto the faceplate upstream of the vane assembly.

The angle of attack sensor further comprises a faceplate heaterpositioned on an inner surface of the faceplate and extending around thevane assembly, and wherein the bearing support cage comprises an outerbearing bore configured to accept the first bearing and an inner bearingbore configured to accept the second bearing, the outer bearing bore andthe inner bearing bore being axially aligned, and wherein the bearingsupport cage provides a direct thermal conduction path from thefaceplate heater to the rotational position sensor.

The bearing support cage further comprises: an outer support adjacentthe central opening, the outer bearing bore extending through the outersupport; and an inner support adjacent the rotational position sensor,the inner bearing bore extending through the inner support; a supportingleg extending from the outer support to the inner support; and a supportcavity between the outer support and the inner support.

The outer bearing bore and the inner bearing bore are axially alignedsuch that the tolerance between a center of the outer bearing bore and acenter of the inner bearing bore is less than 0.001 inch (0.0254millimeters).

The outer bearing bore and the inner bearing bore are machined from asingle piece of metal on the same machine without repositioning thefaceplate.

The vane assembly comprises: a vane hub positioned in the centralopening of the faceplate; and a vane connected to the vane hub.

The vane comprises a root connected to the vane hub.

The rotational position sensor is a resolver.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. An angle of attack sensor comprising: a housing having an open endand a closed end; a faceplate positioned on the open end of the housing,the faceplate comprising: an integral bearing support cage that extendsinto the housing and is configured to accept a first bearing and asecond bearing; a periphery at an outer edge of the faceplate; a centralopening; and an exterior surface extending from the periphery to thecentral opening; a vane assembly extending through the central openingof the faceplate; a vane shaft that extends into the housing and isconnected to the vane assembly; and a rotational position sensorconnected to the vane shaft.
 2. The angle of attack sensor of claim 1,wherein the bearing support cage comprises an outer bearing boreconfigured to accept the first bearing and an inner bearing boreconfigured to accept the second bearing.
 3. The angle of attack sensorof claim 2, wherein the outer bearing bore and the inner bearing boreare axially aligned.
 4. The angle of attack sensor of claim 3, whereinthe outer bearing bore and the inner bearing bore are axially alignedsuch that the tolerance between a center of the outer bearing bore and acenter of the inner bearing bore is less than 0.001 inch (0.0254millimeters).
 5. The angle of attack sensor of claim 2, wherein theouter bearing bore and the inner bearing bore are machined from a singlepiece of metal on the same machine without repositioning the faceplate.6. The angle of attack sensor of claim 5, wherein the metal is aluminum.7. The angle of attack sensor of claim 2, wherein the bearing supportcage further comprises: an outer support adjacent the central opening,the outer bearing bore extending through the outer support; and an innersupport adjacent the rotational position sensor, the inner bearing boreextending through the inner support.
 8. The angle of attack sensor ofclaim 7, wherein the bearing support cage further comprises a supportingleg extending from the outer support to the inner support.
 9. The angleof attack sensor of claim 8, wherein the bearing support cage furthercomprises a support cavity between the outer support and the innersupport.
 10. The angle of attack sensor of claim 9, wherein the vaneshaft extends through the outer bearing bore, through the supportcavity, and into the inner bearing bore.
 11. Then angle of attack sensorof claim 1, further comprising a faceplate heater positioned on an innersurface of the faceplate and extending around the vane assembly.
 12. Theangle of attack sensor of claim 11, wherein the bearing support cageprovides a direct thermal conduction path from the faceplate heater tothe rotational position sensor.
 13. The angle of attack sensor of claim11, wherein the faceplate heater comprises a plurality of heatingelements mounted on the faceplate and arranged to provide a higherconcentration of heat to the faceplate upstream of the vane assembly.14. The angle of attack sensor of claim 1, wherein the angle of attacksensor further comprises a faceplate heater positioned on an innersurface of the faceplate and extending around the vane assembly, andwherein the bearing support cage comprises an outer bearing boreconfigured to accept the first bearing and an inner bearing boreconfigured to accept the second bearing, the outer bearing bore and theinner bearing bore being axially aligned, and wherein the bearingsupport cage provides a direct thermal conduction path from thefaceplate heater to the rotational position sensor.
 15. The angle ofattack sensor of claim 14, wherein the bearing support cage furthercomprises: an outer support adjacent the central opening, the outerbearing bore extending through the outer support; and an inner supportadjacent the rotational position sensor, the inner bearing boreextending through the inner support; a supporting leg extending from theouter support to the inner support; and a support cavity between theouter support and the inner support.
 16. The angle of attack sensor ofclaim 15, wherein the outer bearing bore and the inner bearing bore areaxially aligned such that the tolerance between a center of the outerbearing bore and a center of the inner bearing bore is less than 0.001inch (0.0254 millimeters).
 17. The angle of attack sensor of claim 14,wherein the outer bearing bore and the inner bearing bore are machinedfrom a single piece of metal on the same machine without repositioningthe faceplate.
 18. The angle of attack sensor of claim 1, wherein thevane assembly comprises: a vane hub positioned in the central opening ofthe faceplate; and a vane connected to the vane hub.
 19. The angle ofattack sensor of claim 18, wherein the vane comprises a root connectedto the vane hub.
 20. The angle of attack sensor of claim 1, wherein therotational position sensor is a resolver.